This invention relates generally to electrically-modulated fluid control devices and, more particularly, to a variable force solenoid valve assembly equipped with a combined flat spring/diaphragm which isolates the valve sub-assembly from the solenoid sub-assembly for preventing fluid-borne particles from contaminating the magnetic solenoid components.
As is known, solenoid-operated fluid control devices are used in a wide range of electrically controlled systems for controlling the pressure and/or flow rate of fluid discharged from a valve assembly in response to an electrical input signal supplied to a solenoid assembly. In many applications, a valve sub-assembly and a solenoid sub-assembly are integrated into a unitized fluid control device, commonly referred to as a solenoid valve assembly.
In a typical solenoid valve assembly, the solenoid sub-assembly has an armature which acts on, or is coupled to, a valve member in the valve sub-assembly. As is known, movement of the armature is responsive to the magnetic flux generated as a result of the electrical current applied to the electromagnetic windings of the solenoid sub-assembly. Thus, translational movement of the armature causes corresponding translational movement of the valve member for controlling the magnitude of the output pressure of fluid discharged from the valve sub-assembly. More particularly, fluid at an inlet pressure is delivered to an inlet port of the valve sub-assembly such that the position of the valve member regulates an output pressure generated at an output port of the valve sub-assembly as a function of the energized state of the solenoid assembly. Depending upon the particular design of the solenoid assembly, a change in energization level may cause a proportional increase or decrease in the output pressure, one such proportional device is commonly referred to as a "variable force" solenoid valve assembly or "VFS". One example of a conventional variable force solenoid valve assembly is disclosed in commonly owned U.S. Pat. No. 4,947,893 wherein the axially movable armature of the solenoid sub-assembly is coupled to a spool valve that is supported for axial sliding movement within the valve sub-assembly. As is also disclosed in the above-referenced patent, it is common to provide a guide bearing between the armature and spool valve to support and guide the concurrent translational movement thereof.
As in most hydraulic systems, the hydraulic fluid flowing through the valve sub-assembly is typically entrained with ferro-magnetic particles or shavings. Thus, fluid communication between the valve sub-assembly and the solenoid sub-assembly commonly results in the migration of these fluid-borne magnetic particles into the air gaps established between the armature and coil windings and/or other flux conducting components. Since some of the air gaps in solenoid sub-assemblies are calibrated after assembly to ensure precise accuracy, any subsequent contamination by magnetic particles can adversely affect the desired regulation characteristics of the output fluid pressure. In particular, when such contamination occurs, the reluctance of the magnetic flux path controlling movement of the armature may vary significantly, thereby resulting in inaccurate correlations between the applied energization current and the expected output pressure. In many applications, it is desirable to fiuidically isolate or "seal" the solenoid sub-assembly from the valve sub-assembly, to inhibit such contaminant migration. However, achieving isolation between the valve sub-assembly and the solenoid sub-assembly presents a number of significant design challenges.
In an effort to inhibit such particle migration, some solenoid valve assemblies attempt to isolate the electromagnetic components of the solenoid sub-assembly from the valving components of the valve sub-assembly by installing a flexible elastomeric diaphragm between the armature and the valve member for establishing a fluid-tight barrier. However, use of a flexible elastomeric diaphragm still necessitates the use of a separate guide bearing for guiding the axial translatory movement of the armature. Accordingly, there is a recognized need to develop a fluid-tight barrier or seal that effectively isolates the magnetic and fluid control components of the solenoid valve assembly and yet which overcomes the design and installation constraints typically associated with conventional diaphragm and bearing arrangements.